Beam scanning technology, which is typically used to scan a beam of light produced by a light source on a predetermined area of an object to be light exposed or scanned, may have multiple applications. For example, beam scanning technology may be used in image forming apparatuses or in scanning type display devices. In image forming or printing applications, rotatable polygon mirrors are widely used in beam scanning. A polygon mirror, however, when rotated by a spindle motor, tends to vibrate and produce noise. Moreover, polygon mirrors are typically used in unidirectional scanning, which limits the scanning speed that may be achieved.
A scanning unit that may operate without a spindle motor and a polygon mirror may thus be desirable for a reduction in noise. Moreover, a scanning unit that is capable of bidirectional scanning by, for example, using a deflection mirror that vibrates in a sinusoidal fashion, may also be desirable for an increased scanning speed. However, in performing a bidirectional scanning, the scanning synchronization, that is, determining the starting time and/or the position for the scanning may become relatively more complicated. A typical light scanning unit includes a photo-sensor that detects the light beam, which detection is used for defining an effective scanning area and/or to determine the starting time for the scanning. The photo-sensor may be disposed in the vicinity of one or both ends of a scanning area. A light beam reflected from the deflection mirror may be received by the photo-sensor when it reaches an end of the scanning area at which the photo-sensor is positioned. The starting time for, the next scanning may be determined from the detection signal output by the photo-sensor. When unidirectional scanning is performed using a polygon mirror, it is generally easier to determine the starting time for scanning because there is only one scanning direction. However, when a light scanning unit capable of bidirectional scanning is used, the photo-sensor produces two output signals, one from each end, that themselves provides no indication of the scanning direction, thus necessitating a determination as to which of the two output signal is to be referenced in synchronizing the scanning in a particular scanning direction.